There are a number of situations which involve applying printing such as a print image to an article of a conical configuration or an article which has at least a conical portion. Such an article may be for example a container such as a bottle which serves for packaging purposes. In many cases the transition between the actual body of a bottle or similar article and the end of the bottle which has the opening thereof is of a conical configuration. However, in consideration of the large number of shapes which are nowadays often employed precisely in the packaging field, use is also made of containers which are of a substantially conical configuration over the major part of their axial extent and possibly even over their entire length. When at any event using a screen printing procedure, printing is applied to curved surfaces generally by a mode of operation in which the surfaces are rolled against the screen printing stencil. In that operation, in order to guarantee a good print result or a clear print image, the speed at which the surface to which the printing is to be applied is moved during the printing operation corresponds to the speed at which the screen printing stencil is moved. In that respect, the cross-section of the article does not necessarily have to be of a rotationally symmetrical configuration in the region in which the printing or print image is to be applied. It is sufficient that that region of the peripheral surface of the article, to which the printing is to be applied, can be moved with a rolling action against the screen printing stencil, during the printing operation.
From the printing procedure point of view, a conical configuration of an article or a portion thereof, to which printing is to be applied, presents a particularity insofar as the individual regions of different diameters of the conical article or portion move at different peripheral speeds in such a way that, for a given angular speed, the peripheral speed increases with increasing diameter of the respective region of the article. That must be taken into account in relation to the rolling movement as between the article and the screen printing stencil, during the printing operation, with the result that, during the printing operation, the portion of the screen printing stencil which bears the print to be applied to the article performs a movement along a circular arc whose radius decreases with decreasing cone angle, that is to say the angle between the longitudinal axis of the article to be printed upon, and the surface to which the printing is to be applied.
A further particularity in terms of printing on conical or partially conical articles is that, when the article is arranged horizontally, during the operation of applying printing thereto, the portion of the conical surface which is to be provided with the printing in the printing operation and which is disposed opposite the squeegee or doctor member that co-operates with the screen printing stencil, extends at an acute angle relative to the horizontal. A similar point apply when printing on an article when the longitudinal axis thereof extends vertically. As, during the printing operation, the respectively co-operating regions of the screen printing stencil and the article, at any event under the effect of the squeegee or doctor member, extend parallel to each other and normally at a very small spacing from each other but possibly in contact with each other, then, when the article is arranged horizontally or vertically, the screen printing stencil must also be arranged inclinedly in such a way as to correspond to the inclined positioning of the cone surface to be printed upon, at any event if a high-quality print result is to be achieved. That gives rise to certain difficulties, more especially in particular when the articles to be printed upon are transported through the screen printing machine in quick succession and thus at small spacings from each other. In modern machines, in order to achieve an adequate level of productivity, it is the usual practice for the articles to be transported automatically through the printing machine, in particular when a plurality of print items or images are to be successively applied to produce a combined or overall print image on the article. Admittedly, there is theoretically the possibility of eliminating the difficulties caused by the inclined positioning of the surface to be printed upon, by positioning the article in the printing operation in such a way that the respective region of the surface to be printed upon, which is in contact with the screen printing stencil, extends for example horizontally. That also permits the screen printing stencil to be disposed substantially horizontally. However, inclined positioning of the article in the printing station always results in complication in terms of handling of the article in the printing machine, and that either results in adverse effects on the level of productivity or requires the provision of highly complicated pieces of equipment which make the apparatus susceptible to trouble. It is therefore generally to be preferred that, in the printing operation, the article occupies a position in which its longitudinal axis extends at least substantially horizontally, especially as it is frequently the case that, at the same time as printing is applied to the conical surface, printing is also to be applied to cylindrical or other surfaces, in relation to which the use of a stencil which is movable in a horizontal plane is also preferred. In the present day apparatuses, that means that a pivotable screen printing stencil must be arranged inclinedly to correspond to the positioning of the surface to be printed upon, that is to say it must be disposed relative to the horizontal at an angle which is the same as the cone angle of the surface. However that arrangement requires a certain amount cf space to be available in the printing station on each side of the article as the fact that the axis about which the screen printing stencil performs a pivotal movement is inclined corresponding to the cone angle of the article means that the path of movement of the stencil extends at each side of the article to be printed upon into the regions disposed at each side of the article, beside same, with the result that those regions must be left free in the printing operation. That excludes the possibility of the articles being passed through the screen printing apparatus and the printing stations in quick succession, with possibly only a spacing of a few millimeters from each other.